A diagnostic communication protocol used in automotive electronics for unified diagnostic services (UDS) is specified according to the ISO 14229 international standard. These types of diagnostic services allow contacting and maintenance of various control units in a vehicle, with involvement of the session layer and application layer of a field bus system. A vehicle equipped in this way generally includes a diagnostic interface for the so-called on-board diagnosis, which allows a client, referred to as a diagnostic tester, to be connected to the field bus system. It is thus possible, for example, to query the error memory of individual control units or update them with new firmware.
U.S. Pat. No. 8,856,536 B2 describes a method for authenticating a piece of firmware which is to be downloaded to a controller. The method includes signing the firmware or a first part of the firmware with a first private key at a first trusted source and signing the firmware or a second part of the firmware with a second private key at a second trusted source. The method also includes validating the signed firmware or the first part of the firmware using a first public key at the controller and validating the firmware or the second part of the firmware using a second public key at the controller. The method further includes authenticating the firmware if the firmware or the first part of the firmware is validated by the first public key at the controller, and the firmware or the second part of the firmware is validated by the second public key at the controller.